Method for producing a bottom oxide

Abstract

A method for producing a (thick) bottom oxide in a trench structure, having the following steps: providing a substrate having at least one trench structure comprising a bottom and sidewalls; depositing a polysilicon layer on a surface of the substrate, the bottom and the sidewalls; depositing an oxide layer on the polysilicon layer; depositing a nitride layer on the oxide layer; anisotropic dry etching of the nitride layer; thermal oxidation of the polysilicon of the polysilicon layer to produce a thick oxide layer locally; and wet etching; depositing a further oxide layer on the thick oxide layer along at least the bottom and the surface or on the residual oxide along the bottom and the surface and on the sidewalls.

1 . A method for producing a (thick) bottom oxide in a trench structure, comprising:
 providing a substrate with at least one trench structure comprising a bottom and sidewalls;   depositing a polysilicon layer on a surface of the substrate, the bottom and the sidewalls;   depositing an oxide layer on the polysilicon layer;   depositing a nitride layer on the oxide layer;   anisotropic dry etching of the nitride layer;   thermal oxidation of the polysilicon of the polysilicon layer to produce a thick oxide layer locally;   wet etching;   depositing a further oxide layer on the thick oxide layer along at least the bottom and the surface or on the thick oxide layer along the bottom and the surface and on the sidewalls.   
     
     
         2 . The method for producing according to  claim 1 , wherein a spacer made of nitride of the nitride layer remains and/or is formed along the sidewalls during dry etching. 
     
     
         3 . The method according to  claim 1 , wherein nitride of the nitride layer on the bottom and the surface is removed during dry etching and/or wherein the oxide of the oxide layer on the bottom and the surface is exposed during dry etching. 
     
     
         4 . The method according to  claim 1 , wherein oxidation of the bottom exposed by the nitride and of the exposed surface takes place during oxidation. 
     
     
         5 . The method according to  claim 1 , wherein no oxidation takes place along the sidewall and/or in the region of a spacer made of nitride of the nitride layer along the sidewall during oxidation. 
     
     
         6 . The method according to  claim 1 , wherein the polysilicon bonds with the oxide during oxidation to form a thick oxide region at the bottom and/or at the surface; and/or wherein triggering the oxidation takes place at a temperature which also allows oxidation of the polysilicon without causing oxidation of a material of the substrate. 
     
     
         7 . The method according to  claim 1 , wherein a spacer made of nitride of the nitride layer is removed along the sidewall during wet etching; and/or wherein a part of the oxide layer and/or a part of the polysilicon layer are removed during wet etching. 
     
     
         8 . The method according to  claim 1 , wherein wet etching takes place with high selectivity; and/or wherein a buffered etching process is performed during wet etching to remove the oxide along the sidewall; and/or wherein wet etching comprises several wet etching processes. 
     
     
         9 . The method according to  claim 1 , wherein depositing the further oxide layer and/or depositing the nitride layer take place by means of LPCVD technology. 
     
     
         10 . The method according to  claim 1 , wherein the oxide comprises a silicon dioxide and/or SiO 2 . 
     
     
         11 . The method according to  claim 1 , wherein the substrate comprises a silicon material and/or a silicon carbide material and/or an SiC. 
     
     
         12 . The method according to  claim 1 , wherein the nitride comprises a silicon nitride and/or an Si 3 N 4 . 
     
     
         13 . The method according to  claim 1 , wherein the method comprises forming a gate in the trench structure with the bottom oxide. 
     
     
         14 . A semiconductor device, in particular a MOSFET or trench MOSFET with a thick oxide produced by a method according to  claim 1 . 
     
     
         15 . A semiconductor device, in particular a MOSFET or trench MOSFET with a thick oxide, wherein the semiconductor device comprises an SiC substrate with one or more trenches and an oxidized polysilicon at a bottom of the one or more trenches and the surface of the substrate. 
     
     
         16 . The semiconductor device according to  claim 14 , comprising one or more trench MOSFETs arranged in the one or more trenches. 
     
     
         17 . The semiconductor device according to  claim 15 , comprising one or more trench MOSFETs arranged in the one or more trenches.